<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title-haha</title>
    <link rel="stylesheet" href="{{ url_for('static',filename='test.css' ) }}">
</head>
<body>
{% block head %}
<div>
    this head
</div>
{% endblock %}

{% block content %}
this content
{% endblock %}

{% block foot %}
<div>
    this foot
</div>
{% endblock %}
</body>
</html>